The prior art is replete with various package configurations for semiconductor chips. In recent years, the cost of such packages has, in many cases, out distanced the cost of the chips. An inexpensive packaging technique known as "Tape-Automated-Bonding" (TAB) packaging has come into being and has been especially useful with lower cost, low power dissipation integrated circuits. TAB packages employ a web of polymeric material, generally called a carrier tape, to carry beam-lead conductors which provide connections between the chip and the outside world. The carrier tape is incremented past a number of operating stations, one of which places a chip on an inner-cluster of beam-leads, which cluster is then bonded to connecting pads on the chip. The carrier tape is then incremented to a station where the active face of the chip, including the inner lead-bonds is coated with a passivating material. In conventional systems, the tape is then moved to a further station where the outer beam leads are registered with conductive pads on an underlying circuit board and connections are made therebetween.
TAB packaging is, by its nature, inexpensive. Its use, however, has been mainly restricted to low power dissipation circuits as it has been difficult to apply heat sinks to such structures while still maintaining the package's low cost characteristics.
In addition to its low cost, TAB packaging provides an important temperature compensation feature which is not readily apparent. The conventional TAB package is connected to the underlying circuit board only by its outer lead-bonds. Thus, if there is a difference in the expansion/contraction characteristics between the underlying circuit board and the tape carrier, the flexibility of the package enables it to cope with that phenomenon, thus avoiding bond ruptures which might occur in a more rigid packaging system.
One disadvantage of the TAB package is that it is not inherently pluggable (i.e. able to be plugged into a female connecter) without substantial alteration and/or modification of its configuration.
In U.S. Pat. No. 3,846,825 to Budde, a package is disclosed wherein a semiconductor chip is joined to metal patterns on an insulating flexible foil. The combination is mounted on a ceramic wafer which has an opening aligned with the chip. A conductive heat dissipator, on the reverse side of the ceramic wafer, makes contact with the non-active face of the chip--thereby providing a heat sink. In order to make the package "pluggable", the metal conductors on the foil are soldered to corresponding metal conductors extending from pins which pass through the ceramic wafer and are adapted to be inserted into a female connector. Utilization of the pin connections and the metallized support that carries the pins represent an undesirable added cost to the package.
In U.S. Pat. No. 4,147,889 to Andrews et al, another chip carrier arrangement is shown wherein a thin dielectric with beam conductors thereon is formed into a dish shaped receptacle. The chip contact pads are connected to these conductors by "flying" lead bonds. The receptacle has flexible flanges which are used to mount the combination on a circuit board. Since the package is held in place by relatively thin metallic flanges, its heat dissipation characteristics are limited. Furthermore, there is no teaching of any means for making the package pluggable.
In U.S. Pat. No. 4,132,856 to Hutchison et al, an integrated circuit package is described wherein a carrier tape/chip assembly is emplaced on a heat sink. The combination is then encapsulated with the outer bonds being available for interconnection. The encapsulation of the Hutchison et al package eliminates the flexibility features of the TAB package and makes the outer lead bonds much more susceptible to rupture in the event of differential expansion/contraction with interconnected lands on a circuit board.
Accordingly, it is an object of this invention to provide an improved TAB package which enables high power dissipation from an attached chip.
It is a further object of this invention to provide a TAB package which is pluggable.
It is another object of this invention to provide an improved TAB package which is adaptable to differential expansion/contraction at its interconnection points.